DISORDER EFFECTS ON GaP CORE LEVELS STUDIED BY ELECTRON SPECTROSCOPIES

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DISORDER EFFECTS ON GaP CORE LEVELS STUDIED BY ELECTRON SPECTROSCOPIES

G. Dufour, E. Belin, C. Senemaud, A. Gheorghiu, M. Theye

To cite this version:

G. Dufour, E. Belin, C. Senemaud, A. Gheorghiu, M. Theye. DISORDER EFFECTS ON GaP CORE

LEVELS STUDIED BY ELECTRON SPECTROSCOPIES. Journal de Physique Colloques, 1981, 42

(C4), pp.C4-877-C4-880. �10.1051/jphyscol:19814192�. �jpa-00220819�

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JOURNAL DE P H Y S I Q U E

CoZZoque C4, suppZ6ment au nOIO, Tome 42, octobre 1981 page C4-877

DISORDER EFFECTS ON G a p CORE L E V E L S S T U D I E D BY ELECTRON SPECTROSCOPIES

G. Dufour, E. Belin, C. Senemaud, A. ~ h e o r ~ h i u * and M.L. ~ h e ~ e *

Laboratoire de Chimie Physique, associB au C. N. R. S. n O176, Universitd Paris V I , 11, rue Pierre e t Marie C h e

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75231 Paris Cedex 05, France

?+ Laboratoire d r @ t i q u e des SoZides, Equipe de Recherche associ6e a u C.N.R.S.

n0462, Universitg Paris V I , 4, place Jussieu

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75230 Paris Cedex 05, France A b s t r a c t .

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A s t u d y by X-ray i n d u c e d p h o t o e l e c t r o n and Auger e l e c t r o n s p e c t r o s c o p i e s o f P a n d G a c o r e l e v e l s f r o m s l a s h - e v a p o r a t e d c r y s t a l l i n e a n d amorphous Gap f i l m s i s p r e s e n t e d . B e s i d e t h e e f f e c t s o f c o n t a m i n a t i o n t h e r e s u l t s i n d i c a t e t h e e x i s t e n c e o f p a r t i a l c h e m i c a l d i s o r d e r i n t h e amorphous m a t e r i a l .

The e x i s t e n c e of bonds between l i k e atoms i n amorphous f i l m s o f t h e s e m i c o n d u c t o r compound Gap p r e p a r e d by f l a s h - e v a p o r a t i o n h a s b e e n i n f e r r e d from s e v e r a l e x p e r i m e n t a l d a t a : o p t i c a l and t r a n s p o r t m e a s u r e m e n t s ( 1 ) EXAFS ( 2 ) a n d s o f t X-ray s p e c t r o s c o p y r e s u l t s ( 3 ) . As c o r e l e v e l s b i n d i n g e n e r g i e s a r e s e n s i t i v e t o t h e c h a r g e d i s t r i b u t i o n a r o u n d t h e a t o m , m o d i f i c a t i o n s o f P and Ga p h o t o e l e c t r o n (XPS) and Auger s p e c t r ' a a r e e x p e c t e d when g o i n g from c r y s t a l l i n e t o amorphous Gap due t o t h e p r e s e n c e o f Ga - Ga o r P-P bonds i n t h e amorphous sam- p l e s . However e a r l i e r i n v e s t i g a t i o n s on c o r e l e v e l s by p h o t o e m i s s i o n f o r amorphous and c r y s t a l l i n e Gap p r e p a r e d by s p u t t e r i n g d i d n o t g i v e e v i d e n c e f o r wrong bonds ( 4 ) w i t h o u t e x c l u d i n g t h e p r e s e n c e o f 5-10%

o f s u c h bonds ( 5 ) .

We p r e s e n t i n t h i s p a p e r a c o m p a r a t i v e s t u d y o f P and Ga c o r e l e v e l s f r o m amorphous and c r y s t a l l i n e f l a s h - e v a p o r a t e d Gap f i l m s by b o t h p h o t o e l e c t r o n and Auger s p e c t r o s c o p i e s .

E x p e r i m e n t s

.-

The s a m p l e s w e r e t h i n l a y e r s d e p o s i t e d b y f l a s h e v a p o r a - t i o n o f c r y s t a l l i n e powder u n d e r u l t r a h i g h vacuum on Mo s u b s t r a t e s m a i n t a i n e d a t room t e m p e r a t u r e . The c r y s t a l l i n e f i l m w a s o b t a i n e d b y i n s i t u vacuum a n n e a l i n g a t 550°C.The s a m p l e s were s t o i c h i o m e t r i c w i t h i n a few % a s c o n t r o l l e d by d b a c k s c a t t e r i n g . The t r a n s f e r i n t o t h e e l e c t r o n s p e c t r o m e t e r w a s made u n d e r d r y a i r . The e l e c t r o n s p e c t r a ,

i n d u c e d by t h e r a d i a t i o n e m i t t e d from a n A 1 anode bombarded by 1 2 keV e l e c t r o n s , were r e c o r d e d by means o f a n e l e c t r o s t a t i c h e m i s p h e r i c a l a n a l y s e r o p e r a t e d a t a r e s o l u t i o n o f 7 . 1 0 - 4 . Under o u r e x p e r i m e n J a 1 c o n d i t i o n s , t h e sampled d e p t h i s e s t i m a t e d t o b e a b o u t 1 0 t o 50 A.The s h i f t due t o c h a r g i n g e f f e c t was t a k e n i n t o a c c o u n t by m e a s u r i n g a l l t h e p e a k s r e l a t i v e t o C 1s w h i c h e n e r g y r e f e r r e d t o t h e Fermi l e v e l was t a k e n a s 2 8 5 . 1 eV ( G ) . G r a z i n g - i n c i d e n c e X-ray r e f l e c t o m e t r y and s p e c t r o s c o p i c e l l i p s o m e t r y r e s u l t s b o t h showed t h e p r e s e n c e o f a SU-,

p e r f i c i a l o x i d e l a y e r on amorphous Gap f i l m s . T h i s l a y e r w a s a b o u t 16 A t h i c k and had a v e r y low a v e r a g e e l e c t r o n i c d e n s i t y ; moreover t h e i n - t e r f a c e w i t h u n o x i d i s e d amorphous Gap was p r o b a b l y complex. However- t h e n a t u r e o f t h e l a y e r was i m p o s s i b l e t o d e t e r m i n e f r o m t h e s e e x p e r i - ments ( 7 ) . C o n t a m i n a t i o n (C a n d 0 ) was t o o h i g h t o o b t a i n a n y v a l u a b l e i n f o r m a t i o n a b o u t t h e v a l e n c e band s t a t e s b u t low enough n o t t o a l t e r t h e c o r e l e v e l s p e c t r a s i g n i f i c a n t l y , a s we s h a l l s e e .

R e s u l t s

- -

F i g . 1 shows t h e Ga L 3 M 4 , i M 4 , 5 Auger e l e c t r o n s p e c t r a from amorphous and c r y s t a l l i n e Gap. A s r e p o r t e d by G . S h i i r l ( 6 ) , t h e L3M4,5M4,5 Auger s i g n a l from m e t a l l i c G a c o n s i s t s i n two main components s e p a r a t e d by 3 . 7 e V ; i n Ga203 t h e y a r e s h i f t e d by 5 . 7 eV t o w a r d s l o w e r k i n e t i c

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814192

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JOURNAL DE PHYSIQUE C4-878

e n e r g i e s . F n r c r y s t a l l i n e Gap, t h e Auger s i g n a l i s s i m i l a r t o t h e p u r e Ga one b u t s h i f t e d by 2 . 6 eV t o w a r d s l o w e r k i n e t i c e n e r g i e s . The a d d i - t i o n a l s t r u c t u r e o b s e r v e d o n t h e s p e c t r u m f o r amorphous Gap c a n be a t - t r i b u t e d t o Ga20g a c c o r d i n g t o Shijn v a l u e s . T h i s r e s u l t i n d i c a t e s t h a t o n l y t h e amorphous sample c o n t a i n s a non n e g l i g i b l e p o r p o r t i o n o f o x i d e

Countrng rote

I

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^..-is

1060 1070

K~netrc E n ~ r g y ( e V ) F i g u r e 1

Ga L3M4, 5 M 4 , s p e c t r a f r o m c-Gap ( u p p e r c u r v e ) a n d a-Gap (lower curve)

B e s i d e t h i s c o n t a m i n a t i o n e f f e c t , a

+

0 . 8 eV s h i f t i n k i n e t i c e n e r g y i s o b s e r v e d b e t w e e n t h e Auger s i g n a l s o f a-GaP and c-Gap. T h i s s h i f t c a n n o t b e a t t r i b u t e d t o t h e p r e s m c e o f Ga203,whose c o n t r i h i i t i o n a t t h e

-

r e l g v a n t e n e r g i e s i s v e r y 1 o w . A ~ i t o c c u r s t o w a r d s t h e p u r e Ga s i g n a l , we c a n i n t e r p r e t t h i s s h i f t by t h e p r e s e n c e o f Ga-Ga bonds i n t h e amorphous s a m p l e .

The b i n d i n g e n e r g i e s o f Ga a n d P c o r e l e v e l s deduced f r o m XPS s p e c t r a a r e g i v e n i n t a b l e 1 . T h e Ga a n d Ga7O3 c o r r e s p o n d i n g e n e r g i e s , - -

n ~ e a s u r e d by ShGn ( 6 ) a r e a l s o r e p o r - t e d . The p r 6 c i s i o n o n t h e a b s o l u t e . . a l u e s i s i 0 . 2 eV b u t t h e s h i f t s c a n be e s t i m a t e d w i t h i n 2 0 . 1 eV.

The p r e s e n c e o f Ga203 on t h e amorphous s a m p l e , a s r e v e a l e d by t h e Auger s p e c t r u m , i s r e s p o n s i b l e f o r t h e s p r e a d i n g t o w a r d s h i g h e r b i n d i n g e n e r g i e s o f t h e l i n e s o b s e r - ved when g o i n g f r o m c-Gap t o a-Gap

( f i g . 2 shows t h e G a 3d l i n e ) . B e s i - d e s t h i s c o n t a m i n a t i o n e f f e c t , a s y s t e m a t i c s h i f t o f t h e p e a k s i s o b s e r v e d t o w a r d s l o w e r b i n d i n g e n e r - g i e s . The v a l u e s o f t h l s s h i f t i s a l m o s t c o n s t a n t ( 0 . 2 eV) a n d o c c u r s t o w a r d s t h e p o s i t i o n o f t h e p u r e Ga l i n e ( T h e a p p a r e n t h i g h e r s h i f t o f t h e 3p1,2 l i n e i s a n a r t e f a c t d u e t o t h e l a c k o f resolution o f t h e 3p d o u b l e t j n a-Gap)

.

T h i s r e - s u l t a r g u e s a g a x n i n f a v o u r o f t b e e x i s t e n c e o f Ga-Ga bonds i n t h e amorphous s a m p l e s o f Gap.

T a b l e 1.- B i n d i n g e n e r g i e s i n eV , r e f e r r e d t o t h e F e r m i l e v e l ( s e e t e x t )

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Counting rate

B~nding Energy ( Q V ) Î Î Î

135 130 125

F i g . 2

.

^Ga3d spectra from c-GaP(upper Binding Energy ( eV) curve) and a-GaP(1ower curve)

Fig.3. P 2p spectra from c-GaP(upper curve) and a-GaP(1ower curve)

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M o r e o v e r , t h e a l m o s t e q u a l s h i f t o f t h e 2p a n d 3d l e v e l s e x p l a i n s why t h e a t o m i c X-ray e m i s s i o n l i n e Ga L a ( 3 d + 2 p 3 , 2 ) was f o u n d i d e n t i -

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c a l i n p o s i t i o n i n t h e c r y s t a l l i n e and amorphous Gap f o r m s ( 3 ) .

The mean p o s i t i o n o f t h e 2 s a n d 2p l i n e s o f p h o s p h o r u s a r e n o t a f f e c t e d by d i s o r d e r , i n t h e l i m i t s o f e x p e r i m e n t a l e r r o r . The P 2p l i n e i s shown f i g u r e 3 . P 2p l i n e s f r o m o x i d i z e d p h o s p h o r u s , s i t u a t e d beyond 1 3 3 eV ( 8 ) h a v e a n e g l i g i b l e c o n t r i b u t i o n t o o u r s p e c t r a and c a n n o t p e r t u r b t h e s h a p e and t h e w i d t h o f t h e o b s e r v e d l i n e s . A n e a r l y symme+ric b r o a d e n i n g o f t h e 2 s a n d 2p l i n e s i s o b s e r v e d f o r t h e amorphous s a m p l e . The a b s e n c e o f a n y s h i f t o f t h e P l i n e s i s d i f f i c u l t t o e x p l a i n i f a c e r t a i n d e g r e e o f c h e m i c a l d i s o r d e r e x i s t s i n t h e sam- p l e s ? as s u g g e s t e d by t h e b e h a v i o u r o f t h e Ga l i n e s , u n l e s s t h e c o r r e s - p o n d l n g l i n e s f o r p u r e P a r e v e r y c l o s e t o t h e l i n e s f o r t h e compound.

The p r e s e n c e o f P-P bonds i s on t h e o t h e r hand c o n s i s t e n t w i t h a b r o a - d e n i n g o f t h e s e l i n e s .

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.

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I n c o n c l u s i o n , a l t h o u g h t h e c o r e l e v e l p h o t o e m i s s i o n a n d Auger s p e c t r a show e v i d e n c e f o r c o n t a m i n a t i o n e f f e c t s , a c o m p a r i s o n b e t w e e n t h e r e s u l t s o b t a i n e d o n amorphous a n d c r y s t a l l i n e Gap s a m p l e s p r e p a r e d by f l a s h - e v a p o r a t i o n c l e a r l y i n d i c a t e s t h e e x i s t e n c e o f p a r t i a l chemi- c a l d i s o r d e r i n t h e amorphous c a s e . The p h o t o e m i s s i o n and Auger G a l i n e s a r e s h i f t e d t o w a r d s t h e p u r e Ga l i n e s , s u g g e s t i n g t h e p r e s e n c e o f a n a p p r e c i a b l e p r o p o r t i o n o f Ga-Ga b o n d s . The photoemi*ssion P l i n e s on t h e c o n t r a r y a r e n o t s h i f t e d b u t s l i g h t l y b r o a d e n e d , t h e r e f o r e t h e e v i d e n c e f o r P-P bonds i s l e s s c l e a r . T h e p r e s e n t r e s u l t s c o n f i r m t h o s e a l r e a d y o b t a i n e d by o t h e r e x p e r i m e n t s o n s i m i l a r s a m a l e s . They a r e

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C4-880 JOURNAL DE PHYSIQUE

however in contradictifr with those obtained on sputtered anorphous Gap samples (4), which showed no evidence for chemical disorder. This may just reflect differences in the structure of the two types of samples prepared by different methods.

References

1. A-GHEORGHIU and M.L.THEYE. J.non Cryst. Solids 35-36 (1980) A.GHEORGHIU and M.L.THEYE. Phi1.Mag.B (1981) To be published.

2. M. L.THEYE, A-GHEORGHIU, H. LAUNOIS. J. Phys. C: Solid State 1361980) 6569 3. S.ZUCKERMAN, E.BELIN, C.SENEMAUD, A.GHEORGHIU, M.L.THEYETP~OC. of

the Inter. Conf. on X-Ray processes and Inner Shell Ionization.

Stirling. 1980.

4.N.J.SHEVCHIK3 J.TEJEDA, W.CARDONA. Phys.Rev. (1974) 2627.

S.L.LEY, M.CARDONA, R.A.POLLAK. in "Photoemission in Solids". T o ~ i c s in Applied Physics "01.

27

ed. L.LEY and M.CARDONA (Springer verlag Berlin 1979) p.103.

E.G.SH~N. J.~lectron Spectrosc. 2 (1973) 75.

7.J.PERNASY M.ERMAN, J.B.THEETEN, F.SIMONDET, A.GHEORGHIU, M.L.THEYE, L.NEVOrI. To be published in Thin Solid Films.